全文获取类型
收费全文 | 115488篇 |
免费 | 1550篇 |
国内免费 | 1437篇 |
专业分类
测绘学 | 3305篇 |
大气科学 | 7930篇 |
地球物理 | 21825篇 |
地质学 | 44795篇 |
海洋学 | 9342篇 |
天文学 | 22901篇 |
综合类 | 2361篇 |
自然地理 | 6016篇 |
出版年
2022年 | 622篇 |
2021年 | 1050篇 |
2020年 | 1121篇 |
2019年 | 1250篇 |
2018年 | 7812篇 |
2017年 | 6917篇 |
2016年 | 5590篇 |
2015年 | 1585篇 |
2014年 | 2696篇 |
2013年 | 4516篇 |
2012年 | 4109篇 |
2011年 | 7073篇 |
2010年 | 6104篇 |
2009年 | 7293篇 |
2008年 | 6186篇 |
2007年 | 6965篇 |
2006年 | 3633篇 |
2005年 | 2938篇 |
2004年 | 2988篇 |
2003年 | 2872篇 |
2002年 | 2641篇 |
2001年 | 2034篇 |
2000年 | 2031篇 |
1999年 | 1555篇 |
1998年 | 1625篇 |
1997年 | 1467篇 |
1996年 | 1248篇 |
1995年 | 1245篇 |
1994年 | 1047篇 |
1993年 | 1010篇 |
1992年 | 937篇 |
1991年 | 970篇 |
1990年 | 938篇 |
1989年 | 818篇 |
1988年 | 755篇 |
1987年 | 885篇 |
1986年 | 779篇 |
1985年 | 949篇 |
1984年 | 1071篇 |
1983年 | 1034篇 |
1982年 | 954篇 |
1981年 | 910篇 |
1980年 | 815篇 |
1979年 | 750篇 |
1978年 | 728篇 |
1977年 | 622篇 |
1976年 | 633篇 |
1975年 | 616篇 |
1974年 | 590篇 |
1973年 | 658篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
12.
13.
14.
15.
The effects of natural fish oil,DHA oil and soybean lecithin in microparticulate diets on stress tolerance of larval gilthead seabream(Sparus aurata)were investigated after 15 days feeding trials.The tolerance of larval gilthead seabream to various stress factors such as exposure to air(lack of dissolved oxygen),changes in water temperature(low)and salinity(high) were determined.This study showed that microparticulate diet with natural fish oil and soybean lecithin was the most effective for in-creasing the tolerance of larval gilthead seabream to various stresses,and that microparticulate diet with natural fish oil and palmitic acid(16:0)was more effective than microparticulate diet with DHA oil and soybean lecithin. 相似文献
16.
17.
18.
Measurement of variations in the radial velocities of stars due to the reflex orbital motion of the star around the planetary-system barycenter constitutes a powerful method of searching for substellar or planetary mass companions. After several years of patient data acquisition, radial-velocity searches for planetary systems around other stars are now beginning to bear fruit. In late 1995 and early 1996, three candidate systems were announced with Jovian-mass planets around solar-type stars. The current paradigm for low-mass star formation suggests that planetary systems should be able to form in the circumstellar disks surrounding young stellar objects. These newly discovered systems, and other discoveries which will soon follow them, will test critically our understanding of the processes of star- and planet-formation. We review the techniques used in these radial-velocity searches and their results to date. We then discuss planned improvements in the surveys, and the prospects for the next 20 years. 相似文献
19.
H. A. Harutyunian 《Astrophysics》1996,39(4):370-374
The Voigt function and its derivatives are represented by means of series in Hermite polynomials. The equations obtained can be used both for numerical calculations of these functions and for analytical research.Translated from Astrofizika, Vol. 39, No. 4, pp. 619–625, October–December, 1996. 相似文献
20.
AN ILLUSTRATIVE STUDY ON LOCAL LANDSCAPEAND ITS LONG-TERM CHANGES BASED ON IKONOS AND HISTORICAL AERIAL PHOTO 总被引:2,自引:0,他引:2
RUANRen-zong ErieCELLISt 《中国地理科学(英文版)》2004,14(2):162-169
Nowadays, the research works on landscape at fine scales using high-resolution images are uncommon.This research is based on the analysis of the combination of remote sensing data (1KONOS imagery acquired in 2002 and historical aerial photo taken in 1942). In the paper, the ecotopes in Qiujiadou and Xishao villages in Yixing City of Jiangsu Province in 1942 and 2002 were compared and landscape changes as well as the causes of the considerable changes were analyzed. It was found that the ecotope changes were at greater level in some aspects such as water surface and perennial vegetation coverage etc. This study at fine scale is globally significant for the rural areas, especially for the subsistence agricultural land, which occupies larger percentage in the earth. And it analyzes the structure of landscape based on a new landscape classification system--stratifications method. 相似文献